Furo-coumarins in combination with blacklight are being used as chemotherapeutic agents in the treatment of diseases in man such as Xeroderma pigmentosum and Psoriasis. These compounds are also commonly occurring in man's natural and artificial environment. The possible exposure of the human population to these compounds is, therefore, relatively high and cause for concern. Systematically, little information is known about the comparative mutagenic, carcinogenic and teratogenic effects of the furo-coumarins. It would be interesting to determine the comparative mutagenicity of one of the furo-coumarins, 8- methoxypsoralen (8-MOP) with various combinations of blacklight in a variety of microbial systems and to determine the type of genetic alteration caused by 8-MOP in each region. In the later stages of the project, the investigation will be expanded to other furo-coumarins in order to determine whether there is a relationship between the mutagenicity and chemical structure of the furo-coumarins.